Sound Track: Microphone Types

Dr. Robert G. Nulph
August 2000

Has the selection of microphones offered by your favorite electronics store ever overwhelmed you? Have you stared in awe at the vast array of silver or black, big or small, expensive or cheap microphones available to you? Have you wondered about HiZ versus LowZ, dynamic versus condenser, cardioid versus omni-directional or shotguns and lavaliers versus handheld and boundary mikes? Throughout this column, we will take a look at impedance, the two major ways microphones work, microphone pickup patterns and microphone styles. So sit back, relax and proceed through this quick look into the sometimes confusing world of microphone choice.

Before you choose the style of microphone you d like to use, you have to know what impedance of microphone is compatible with your camcorder. Your system might require a HiZ microphone input. Impedance is the resistance to the flow of electrical current in a circuit or element. We measure impedance in ohms, a unit of resistance to current flow. The lower the impedance, the better the microphone or recording device.

Most older consumer camcorders have a high impedance (HiZ) microphone jack meant to be used with high impedance microphones. These microphones range in impedance from 600-1400 ohms. HiZ microphones are very sensitive and require very little amplification, which is why less sophisticated consumer equipment is designed for them. They are, however, susceptible to hum and electronic noise and can be used only with a very short microphone cable.

Low impedance microphones, with an impedance level of 100-600 ohms, have become the norm in video production. Even much of today s consumer equipment now has low impedance inputs to allow you to use professional microphones. Using these professional microphones with low impedance gives you two advantages: (1) They are not as affected by electronic hums and noises that can be caused by fluorescent lighting or electric motors and (2) you can use long cables without worrying about outside interference.

If you buy a microphone and plug its cable into your camcorder and nothing happens, it may be due to an impedance mismatch. If your camcorder requires a HiZ microphone and all you have are professional mikes, don t despair. You can purchase an inexpensive LowZ to HiZ transformer. Plug your microphone cable into the transformer and the transformer into your camcorder. You should now be able to use any professional microphone with your system. Now that we ve gotten impedance choice out of the way, we can move on to the other mike variables.

Most microphones fall within one of the two major families: dynamic or capacitor (condenser) microphones. The dynamic microphone has a fixed magnet, a diaphragm that moves when sound hits it, and a coil attached to the diaphragm. When the diaphragm moves, the coil moves, making changes in the magnetic field. These changes generate voltage through the microphone cable to the recorder, amplifier or speakers (see Figure 1).

The dynamic microphone has a number of attributes that you need to take into account when deciding on the type of microphone you need. This type of microphone is extremely durable. Dynamic mikes can tolerate wide temperature ranges and humidity as well as take a great deal of abuse. I have seen them dropped, banged around, used in the dead of winter, in the high heat of a tropical rain forest and even (believe it or not) used as a hammer (not recommended), all without affecting the mike s ability to record high quality audio. Dynamic mikes are also fairly inexpensive. Good quality dynamic microphones like the Shure SM58 costs around $200. Lower quality dynamics run as low as $77. Even the extremely good dynamics rarely cost more than $350.

Another attribute of the dynamic mike is its ability to provide a warm, rounded sound for vocals and yet take the abuse of recording high impact sounds such as drums and screaming voices. Many lead singers in rock bands use the hand held dynamic because of its ruggedness and its ability to pick up a wide range of sounds from screams to whispers. However, the dynamic microphone has a less accurate sound reproduction than the condenser.

A final advantage of the dynamic is that it requires no outside power. Plug it into your recorder or sound system and go. No batteries or power supplies needed. In video work, the dynamic microphone is ideal for on-camera interviews, recording very loud sound sources and crawling around the toughest terrain.

The capacitor or condenser microphone uses variations in voltage within a capacitor. The capacitor, which is capable of holding an electrical charge, is made up of two parallel plates, one fixed and one moving, separated by a small space. When sound waves hit the movable plate, it vibrates and causes a change in the amount of voltage held by the capacitor. This change in voltage is sent down the wires to be recorded or amplified through speakers (see Figure 2).

The condenser microphone has a number of attributes that are important for the videographer to consider. The condenser mike is not so rugged as the dynamic, and the more expensive models are downright delicate. They range in price from around $100 for a basic condenser to well over $5,000 for a high-end studio mike. Although the condenser is usually more expensive, its frequency response and true sound rendering make it ideal for the videographer seeking the best fidelity.

You will have to consider one other attribute when purchasing a condenser microphone: its need for an additional power source. A battery, or AC power source can provide this additional "phantom" power. If you have a mixing board with phantom power built into the inputs, it will supply power to any mike you plug in. You can purchase a condenser microphone and begin using it right away. However, if you plan to plug a phantom-powered microphone into your camcorder, you ll need to purchase a phantom power unit to supply juice for your mike. Fortunately, most microphones that you would use for field production have a battery space built-in. You just have to remember the batteries.

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